The intended operation, potential, and significance of the present invention are perhaps best illustrated by a short review of the foundational thermodynamic principles of heat engines.
In Sadi Carnot's translated words: “The necessary condition of the maximum is, then, that in the bodies employed to realize the motive power of heat there should not occur any change of temperature which may not be due to a change of volume. Reciprocally, every time that this condition is fulfilled the maximum will be attained. This principle should never be lost sight of in the construction of heat engines; it is its fundamental basis. If it cannot be strictly observed, it should at least be departed from as little as possible.”
Rudolf Diesel showed that the thermal efficiency of a heat engine is directly related to the rate and temperature at which heat is added to the engine's working fluid. He used the ideal gas law, pV=nRT, to show that adding heat to the working fluid while simultaneously maintaining it at a constant bulk temperature turns the most heat into work, avoiding Carnot's “useless re-establishment of equilibrium in the caloric.” The working fluid maximum bulk temperature is achieved solely by mechanical compression. This temperature must be above the auto-ignition temperature of the selected fuel. The rate at which fuel of a specific heating value is injected is the rate at which the heat released by the self-ignited combustion of that fuel maintains a constant bulk temperature. Following the gas law, the bulk gas experiences a pressure decrease as the piston withdraws. The pressure decrease varies smoothly, not at a constant rate as would be accommodated by a fixed fuel delivery rate. However, admitting the combustible to maintain temperature results in net work since pressure remains higher than during the compression stroke. Gradually admitting the combustible as prescribed results in maximum fuel economy since heat transfer from the bulk gas is minimized by not letting its temperature rise by combustion.
An indicated efficiency (excluding friction and pumping losses) of well over 60% is theoretically possible. Restated, much more than 60% of the available heat can be converted into mechanical work and much less than 40% of the heat would be lost. This is a conservative percentage according to Diesel himself. (Even without the drive to reduce emissions, raising efficiency is a powerful economic incentive to improve fuel injector technology. Presently, diesel truck engine thermal efficiency is approximately 40% while gasoline engines are 25% to 30%, the lower gasoline engine range being matched by Diesel's prototype over 100 years ago as he reported in his lecture of 1897.)
Achieving Diesel's seemingly simple prescription to maintain the working fluid at a constant temperature as heat is added has proven to be anything but simple. Details on just how formidable this task has been can be read in patents and papers such as Ganser. There are complexities with respect to 1) liquid fuel atomization, vaporization, mixing, and combustion, 2) engines where the load and speed are constantly changing, such as in ground vehicles, and 3) attempting to force a non-linear device such as a solenoid to behave in a less non-linear fashion.
Pollutant formation is controlled by combustion complexities. One of the most important ways to control combustion and thereby control both fuel economy and pollutant formation is the method of admitting the combustible; the method of injecting fuel into the hot, compressed, swirling, oxygen-rich air inside the combustion chamber. Diesel himself noted in his U.S. Pat. No. 608,845 that soot was generated from his coal dust fuel.
The progress of diesel engine pollutant control includes a steady rise in the pressure of the liquid fuel supplied to the injectors. The state of the art is generally in the range of 35,000 psi, with yet higher pressures under consideration.
Much technical literature and prior art patents disclose that metering very quick jets or pulses of standard number two liquid petroleum diesel fuel helps to reduce pollutants. High pressure improves fuel atomization and, for very quick jets, mixes enough finely atomized fuel with fresh, oxygenated air.
To admit the combustible both gradually and/or in quick jets as the engine load and speed vary while minimizing emissions, the means of control within the injector preferably has continuously variable control over both stroke and speed of the valve element with respect to time. Restated, such an injector should rate shape the injected fuel such that the bulk temperature of the working fluid (air followed by combustion gases) does not increase as the fuel is injected over all speed and load conditions of the engine, while simultaneously being able to inject very short individual pulses.
Much creative and ingenious innovation has gone into improving control over diesel fuel injection, which is apparent in trade magazines, society journals, scholarly papers, patents, etc. Ultimately, these efforts are limited by the physics of the two main electrical control technologies used to date: solenoids and piezo-electric ceramics, hereinafter piezo. Solenoid injectors date at least as far back as Gaff in 1913 while piezo injectors date at least from Bart in 1977. Thus, both piezo and solenoids have had the benefit of sustained attention to their limitations. Well into the piezo injector era, Benson et al in 2008 show that piezo has not yet fully replaced solenoid technology.
Ideally, fuel is injected at continuously variable flow rate(s) that match engine needs continuously throughout each injection event, regardless of engine load and speed. The word “programmable” describes the technology of the present invention that is capable of almost arbitrary rate shaping, each rate shape being changeable without altering the injector itself, thereby permitting a closer approach to Diesel's prescription.
In context here, Alexander Graham Bell's invention of the telephone deserves special mention. Bell leapfrogged intensely creative attempts to use the solenoid-operated telegraph to re-create intelligible speech. Key features of his telephone included the ability of the earphone diaphragm to quickly and proportionally follow its undulating analog electrical signal input-exactly the same feature required of a programmable diesel fuel injector that exercises continuous control over the rate at which fuel flows.
Solenoids offer durability, but are unsuitable for programming. Their key characteristic is that the mechanical motion can never be proportional to electrical input. While durable and reliable, neither intelligible speech nor ideal fuel rate shapes can be reproduced by the solenoid. By its operating principle, when a magnetic flux above a threshold value crosses an air gap, its two poles accelerate toward each other, closing the gap until, eventually, they impact each other and, depending on design details, bounce back. The force that accelerates the two poles is inversely proportional to the square of the gap between them, making velocity or position control difficult. Thus, the solenoid is either open, closed, bouncing, or transitioning between these states at a more or less uncontrollable rate.
Although their characteristic is occasionally described as “switching,” implying telegraph-like ON-OFF behavior, unlike telegraphs, piezos offer speed and infinitely adjustable displacement within their range, permitting continuous control. The key feature of this technology is that mechanical expansion is proportional to applied voltage. Piezo force and displacement are akin to thermal expansion except electrically controllable and much, much faster. Piezos can be used to reproduce intelligible speech or to rate shape injected fuel, but only for a while. Their critical defect is susceptibility to performance degradation as noted in U.S. Pat. Nos. 5,875,764, 7,159,799, and 7,262,543, MIL-STD-1376, and Cain et al, among many references. This inherent degradation or aging is the Achilles heel of piezo technology, disabling its use in a durable, programmable diesel injector. When lightly loaded to get reasonable life, piezos can offer a telegraph-style ON-OFF speed improvement over solenoids, enabling the faster and smaller multiple pulse injections currently being used to reduce in-cylinder formation of diesel emissions. Despite its speed and proportionality, limiting piezo to telegraph-like behavior to get a reasonable working life makes this approach less than ideal for rate shaping fuel injection.
The US Navy developed a magnetostrictive material that applied a little-known intermetallic alloy of iron and the rare earths terbium and dysprosium, hereinafter “REA”, for use in sonar—it is the magnetic equivalent of piezo.
The REA couples a magnetic input to a mechanical output. This alloy offers speed, infinitely adjustable displacement within its range, and the durability to survive on an engine cylinder head. The key feature of this technology is that mechanical expansion is proportional to the current sheet circulating around it. Magnetostrictive displacement and force are akin to thermal expansion except magnetically controllable and much, much faster as noted in Dapino et al and Faidley et al. REAS can be used to reproduce intelligible speech or to rate shape injected fuel without a durability limit. Performance diminishes as temperature rises, but returns fully as temperature falls, an effect controlled by alloy proportions.
U.S. Pat. No. 7,255,290 (the “'290” patent) discloses a simple key to programmable fuel injection rate shaping. The complete patent, especially the discussion comparing the various means of electromechanical transduction, is incorporated herein by reference. In sum, an REA magnetostrictive transducer featuring high compressive pre-stress combined with few turns in its solenoid coil are the key characteristics. It bears repeating that the REA will inherently survive on an engine cylinder head without performance degradation. This technology is durable.
High compressive stress on the REA improves frequency response (speed) in three ways. The first two ways are material parameters intimately related to the mechanism of magnetostrictive transduction, both of which are positively affected by high compressive stress.
First, high stress reduces the variable magnetic permeability of the REA, reducing electrical inductance. Less inductance lowers the voltage needed to dynamically vary the current sheet circulating around the REA element.
Second, high stress increases the variable Young's modulus of the REA. Increased stiffness of the REA element increases its frequency response.
Third, at high compressive stress, the same force requires an REA element of less cross-sectional area. As a result, less of its magnetically-originated mechanical force is expended in accelerating its own mass to position internal valve elements, thereby increasing frequency response yet further.
The theoretical proportionality and high speed of the REA magnetostrictive transducer have now been proven by test. Early data from this testing have been published by Bright et al. The test transducer was subject to fuel pressures of 15,000 to 25,000 psi to compress the REA and then electrically energized to take data. Detailed testing continues, particularly testing at yet higher fuel pressure.
The '290 patent uses transducer output to control a traditional hydromechanical section that masks the full power and capability of magnetostrictive technology. In other words, the conventional needle and related plumbing are not well matched to nor do they take advantage of the greatly improved transducer capabilities. Simulation and preliminary testing indicate that this technology provides sufficient control authority to replace all other sources of motive power, particularly fuel pressure. That is, it is capable of direct drive.
Following tradition, the '290 patent uses a spring to preload the REA, lowering frequency response. Springs that can apply the required compressive preload at the required stiffness and survive the fatigue requirements have either relatively large diameter, as in the case of disc springs, or long length, as in the case of coil springs. Conserving diameter is preferred for any device on an engine cylinder head but this conflicts directly with the transducer advantage of locating the spring closer to the injector tip that protrudes into the combustion chamber. Even though a spring that increases diameter would have the advantage of being shorter with less mass to accelerate, it may be very difficult to fit it onto a particular engine. Friction and fretting wear on the edges of this type of spring would limit injector life.
The second kind of spring adds length and bulk which also add much more mass to be accelerated, lowering frequency response. Besides mass, moving elements that are relatively long and thin tend to bend and vibrate and therefore would need to be guided, adding fabrication cost. The spring itself will interact with the deflections and speed required, slowing the valve element and introducing undesired motions.
Design and fabrication complexity are introduced by the need to compress any spring during assembly. This preload must be applied without subjecting the brittle REA rod to any twist or misaligned end pieces. The mechanism would need to apply the preload carefully and lock it in place for the life of the injector.
The second tradition followed by the '290 patent is to use transducer output to control the drain and fill of a control volume which in turn controls the pressure balance across a needle. Lower frequency response results due to draining and filling time delays plus any inertia and compliance of the control volume. For these same reasons, precision is reduced.
Thirdly, the needle is ballistic and can bounce or oscillate uncontrollably, behavior that again resembles a telegraph. Frequency response and precision are reduced accordingly.
Finally, the '290 patent has no thermal compensation. Expansion differences between the REA and the rest of the injector—critical due to the available displacement—must be compensated for.
The injector of the present invention corrects all of these defects while being shrunk and simplified. Certain critical machining tolerances become unnecessary with this improved configuration. The robust electro-mechanical actuator technology of the present invention provides sufficient electric selectability of continuously variable force and displacement with respect to time thus replacing fuel pressure and achieving valve element speed. This enables fuel injection rates of virtually any necessary shape, including multiple short pulses and/or gradual admission of the combustible fuel from the same injector, wherein the complexity required to form the rate shape is shifted from the simplified mechanical portion of this injector to electrical or electronic means. To achieve fine flow rate control by fine valve element positioning control, it is necessary to disconnect the transducer forces acting on the valve element from the pressure-induced forces that the valve element controls. Since any waveform can be programmed at any time without disturbing the injector or its installation, the injector is termed programmable.
Although, as described hereafter, appearing in the prior art are elements necessary for a programmable diesel fuel injector, none of the prior art discloses an injector that matches an electromechanical transducer with sufficient and precise control authority and frequency response with a suitable hydromechanical section that takes full advantage of such a transducer. In other words, an injector with compensated direct drive does not appear.
Related prior art is cited below for any of the following reasons. The injector of the present invention overcomes the limitations of each citation.
First, related prior art is cited if it features compliance or inertial effects caused by such items as springs or masses that would tend to reduce frequency response. Excess compliance and inertia are made obsolete by the injector of the present invention.
Second, related prior art is cited if a control volume is used, the control volume being used to redirect an outside source of motive power such as fuel pressure. That is, the prior art is cited if a smaller cause and effect is used to control a larger cause and effect, which inevitably lowers frequency response and decreases metering accuracy. In addition to its frequency response, the injector of the present invention has sufficient force and stroke available to control the valve element almost directly, where “almost” is defined as the need to insert thermal compensation.
Third, related prior art is cited if it uses piezoelectric ceramics. The '290 patent details why piezo is not preferred. For all of the different prior art fuel injectors cited below, the '290 patent details how piezos degrade with use, meaning that any injector employing such an actuator is forced to limit stroke and speed to obtain acceptable life. Piezos have been known for decades yet the continuation of the art to rate shape with means that are primarily mechanical, and suffering limited effectiveness as a result, indicates the degree of difficulty that has been encountered in the employment of piezos within fuel injectors. The limited effectiveness of injector control raises emissions and lowers fuel economy.
The tremendous fuel pressure is a potent source of high grade mechanical energy that the prior art has used to assist with the high speed required of the injector by being directed to accelerate and position solid internal mechanical elements. The limitations of prior art electro-mechanical actuator technologies have only permitted them to act more as triggering mechanisms to direct fuel pressure than as modulators of flow rate. Therefore, prior art injectors are either closed, open, or transitioning more or less uncontrollably between these two states. This behavior inherently cannot “gradually admit the combustible” over even a modest load and speed range. Partial rate shaping under specific conditions has been achieved by hydromechanical means, for instance, but the resulting injectors remain inflexible and are more complex and expensive to produce. Thus, rate shaping remains elusive as fuel is merely dumped in, albeit in finer increments but still violating Diesel's prescription that “the combustible is added in such a way, that no increase in the temperature of the gases, consequent upon the process of combustion, takes place, . . . . After ignition, combustion should not be left to itself, but be regulated by an external arrangement, maintaining the right proportion between the pressures, volumes, and temperatures.”
U.S. Pat. No. 4,022,166 claims a needle displacement of 0.006 to 0.010 inches in 30-150 microseconds, but suffers from excess accelerated mass, including its biasing spring 58 which reduces its speed, and the use of a piezo stack. This patent further discloses the benefits of multiple injections per engine cycle.
U.S. Pat. No. 4,175,587 points out that the rate of voltage rise across a piezo stack should be controlled within certain limits to avoid arcing between the positive and negative electrodes interleaved between discs in the stack. Depending on the particular configuration, this limit may restrict the speed of any injector using piezo.
U.S. Pat. No. 4,180,022 discloses 1) a piezo actuator with spring preload, 2) that the rate of voltage rise across the piezo stack may need to be limited to prevent arcing, and 3) that the piezo stack temperature may rise unacceptably due to duty cycle.
U.S. Pat. No. 5,031,841 discloses the sensitivity of exposing a piezo stack to water, a common contaminant in fuel. Water is an electrical conductor. The REA is different; because it contains iron, it will “rust” if continually exposed to water for a long period of time.
U.S. Pat. No. 5,697,554 discloses a piezo actuator with spring preload controlling a low pressure fuel chamber, thus maximizing accelerated mass and minimizing the available stress. It further discloses an outward-opening pintle and is thus subject to coking, gum, and other contaminant build-up.
U.S. Pat. No. 5,779,149 uses the fuel as part of the compensation for thermal expansion differences but it does this by an arrangement where the master piston moves in a direction opposite to the slave piston, thus requiring more fluid and accelerating some of that fluid in a first direction followed by a second direction. It uses springs for preloading a piezo stack and a first chamber filled with low pressure fuel. The springs slow its speed and do not allow the stack to take advantage of the pressure available for preloading.
U.S. Pat. No. 5,810,255 uses two piezo stacks, the second being in a novel way to compensate for thermal expansion by clamping. Material frangibility greatly enhances difficulty.
U.S. Pat. No. 5,860,597 uses a pilot-operated control volume.
U.S. Pat. No. 5,875,632 discloses an arrangement where the master piston moves in a direction opposite to the slave piston, thus requiring more fluid and accelerating some of that fluid in a first direction followed by a second direction.
U.S. Pat. No. 5,875,764 discloses a pilot-operated control volume and further discloses that the “switching” behavior of piezo is subject to aging.
U.S. Pat. No. 5,979,803 discloses 1) the desirability of a needle control mechanism independent of fuel pressure and 2) the inability of a piezo actuator to pressurize fuel.
U.S. Pat. No. 6,079,636 uses either a piezo or magnetostrictive actuator as a pump to pressurize the fuel. Both piezo and magnetostrictive materials mimic the force and stroke of thermal expansion except much faster. However, the low bulk modulus of liquid fuels requires much displacement to raise pressure significantly, meaning it will be difficult for such an actuator to provide meaningful pressure and flow. Besides being complex to fabricate, U.S. Pat. No. 6,079,636 will require big and bulky—and therefore slow—transducers.
U.S. Pat. No. 6,253,736 uses relatively large masses which slow acceleration, a bias spring the mass of which also slows acceleration, and a piezo stack. Impact of a valve element causes a voltage spike to appear, which will cause the performance of the piezo stack to degrade even faster than pointed out in the '290 patent, if it does not crack first.
U.S. Pat. No. 6,499,467 discloses the detrimental effects of needle velocity, impact, and sticking.
U.S. Pat. No. 6,526,864 discloses that the compliance and inertia of a pilot-operated control volume reduces the possible frequency response.
U.S. Pat. No. 6,557,776 discloses 1) a complex mechanism to achieve rate shaping, an initial very short pulse followed by an unrestricted injection flow rate, which will raise the bulk gas temperature, 2) usage of control volumes, and 3) the desirability of providing small spray orifices to increase injection duration at low speed and light load.
U.S. Pat. No. 6,568,602 discloses 1) the desirability of different rate shapes across the spectrum of engine operating speed and load, 2) the desirability of metering accurate, small doses, and 3) that the moving needle valve element is deliberately allowed to impact the piezo stack. Impact causes a voltage spike to appear, which will cause the performance of the piezo stack to degrade even faster than pointed out in the '290 patent, if it does not crack first.
U.S. Pat. No. 6,570,474 shows the basic, simple component arrangement but uses preload springs and limits the REA compressive preload to 5-15 MPa. This ensures that the REA is bulky and has a lower Young's modulus and higher magnetic permeability. The added mass of the preload springs slows it further.
U.S. Pat. No. 6,637,675 discloses a complex injector with two needles.
U.S. Pat. No. 6,758,409 uses pressurized fuel to compensate for thermal expansion differences but employs springs to preload a piezo stack. Voltage is applied to the stack continuously until it is removed for injection to occur by a claimed stroke of up to 0.25 mm. Designing the injector to be closed with voltage applied means that removing voltage may have the unfortunate consequence of allowing continuous injection in the event of a fault that disables that voltage. If the needle opened by traveling in the opposite direction, there would be no need for the stack to be energized to the pre-expanded condition.
U.S. Pat. No. 6,837,221 discloses 1) the desirability of an abrupt end to fuel injection to prevent the formation of unburned hydrocarbon emissions, 2) a pilot-operated control volume, and 3) the undesirability of pilot-operated control valve member oscillations.
U.S. Pat. No. 6,978,770 discloses that rate shaping can relieve the need to recirculate exhaust gas to achieve emissions reduction. However, it also discloses 1) a hollow piezo stack penetrated by its output rod, 2) a spring preload, 3) a pilot-operated control volume that reduces the speed and precision with which the needle can be operated because fuel requires time to flow into and out of the volume, and 4) that piezo stack voltage is permitted to decay passively.
U.S. Pat. No. 7,059,295 discloses the benefits of cavitation, throttling, rate shaping, and multiple injections, but resorts to complexities such as multiple pressures to achieve it.
U.S. Pat. No. 7,077,377 discloses 1) excess mass and 2) that the amount of dead volume has adverse effects on the motional dynamics of the master and slave pistons.
U.S. Pat. No. 7,140,353 discloses a piezo actuator that operates a pilot valve on a control volume.
U.S. Pat. No. 7,159,799 discloses a mechanically complex injector driven by a piezo actuator in which only discrete voltage levels are used, thus limiting its proportionality and resulting in a limited selection of rate shapes. The patent further discloses that actuator lifetime is enhanced by reducing the time at which the injector is at a high energization level.
U.S. Pat. No. 7,196,437 inserts bias magnets in line with the magnetostrictive transducing material. Adding inert material forces the entire transducing member element to lengthen, adding mass to accelerate. Since the bias magnets are made from a different material, column buckling strength is reduced, for which diameter must be increased to compensate. The presence of bias magnets reduces magnetic permeability and therefore reduces electromechanical coupling, forcing input energy requirements to increase in compensation. Bias magnets will add bulk and make handling difficult.
U.S. Pat. No. 7,262,543 discloses a means of ascertaining the deterioration over time of the performance of piezo material.
U.S. Pat. No. 7,334,741 discloses an injector with a mechanical sleeve for achieving a rate shape.
U.S. Pat. No. 7,422,166 discloses that electromagnetic solenoid actuators achieve lower opening force and a slower rise of force over time. This limits speed.
U.S. Pat. No. 7,500,648 discloses a preload spring and excess accelerated mass.
U.S. Pat. No. 7,934,668 discloses an inflexible, mechanically complex injector.
U.S. Pat. No. 7,967,223 discloses the time delays of a hydraulic servo mechanism but then uses an inflexible, mechanically complex injector to overcome the larger and more expensive piezo actuator otherwise envisioned. The patent further discloses use of pressure to assist in needle actuation.
With respect to diesel fuel injector actuators and exhaust system equipment, it is of particular importance that the need for platinum group precious metals be reduced or eliminated. These metals are referred to as precious due to their cost. Precious metals have been used as electrodes in piezo stacks, raising their cost. Within the exhaust system, precious metals are used to catalyze beneficial chemical reactions. Better control over in-cylinder combustion will reduce or may even eliminate the need for their use.
Therefore, it is an object of the present invention to improve upon and overcome the foregoing drawbacks present within prior art devices.
It is an object of the present invention to provide a durable, compact, and programmable diesel fuel injector that can also be retrofitted to existing engines.
These and other objects, features or advantages of the present invention will become apparent from the specification and claims.